Automatic selecting systems



April 2, 195.7 J. E. FLOOD 2,787,666

AUTOMATIC SELECTING SYSTEMS ttprneys April 2 1957 A J. E. FLooD i 2,787,666

AUTOMATIC sELEcTING sYsTEMs Filed July 7. 1954 l I 2 sheets-sheet 2 F/...Z To@ l g. m00 T00/ T002 m03. 7004 Tl c 71//0-A TZ l w44 Y O O O l0 02 f3 v14K 1 A? i, 77 .MW /e/ j l 6 VH N: 'm5 I AUTOMATIC SELECTING SYSTEMS .lohn Edward Flood, Home Hill, London, England, as-

signor to Siemens Brothers & Co. Limited, Loudon, England, a company of Great Britain Application July 7, 1954, Serial No. 441,902

6 Claims. (Cl. 179-,-18)

This invention relates to improved arrangements for the selection of a free one of a number of circuits in a group. Arrangements of this kind are frequently required in telephone systems, the general arrangement being for a particular group to be indicated by suitable means, for example in response to a train of impulses or by a marking denoting the group in which selection is to be made and for a free circuit within the indicated group to be searched for or otherwise selected. The groups however may have no numerical significance.

Means have been proposed for effecting selection of a free circuit within a group electronically by means of cold cathode gas-filled discharge tubes and by making use of the property of negative resistance which such tubes possess over part of their characteristics the anode circuits of a number of vtubes` may be connected over a common impedance, which arrangement ensures that only one tube of the number is tired at any time. One such proposal entailed the use of a cold cathode tube for each circuit to be selected. The arrangements are satisfactory for a small numbery of circuits ibut are liable to be uncertain when -a large number of tubes have a common anode impedance. Other proposals using fewer tubes than there are circuits to be selected have been made but these have not been without the introduction of considerable additional apparatus or complications. The improved arrangements of the present invention are especially suitable when selection has to be made among a large number of circuits by the use of simple arrangements.

In the present invention each circuit of a group in which selection of a free circuit is to be made is represented by the intersection of co-ordinatcs of a plurality of sets of ctn-ordinates and negative resistance devices, by which term we include cold cathode gas-filled discharge tubes operating as above mentioned, thermionic valves or transistors with positive feed-back, and thermistors, are arranged on a co-ordinate basis, there being a number of such devices 'for each set of co-ordinates, one device per co-ordinate and their circuits are so arranged that a device of a co-ordinate of a first set can operate freely when there is a free, circuit connected to the co-ordinate but that operation of a device of a coordinate of a second set is dependent on the prior operation of a device of a co-ordinate ofV the first set. Similarly, if the co-ordinates are three-dimensional, operation of the device of a col-ordinate of the third set is dependent on the prior operation of a device of a coordinate of the second set. Generally, a two co-ordinate basis will be found suiicient one set of co-ordinates being rows and other set of co-ordinates being columns 'and there will be onev devicegassociated with each row and one device associated with each column and the circuits to be selected will be represented by the intersection of a row and a column. References to rows and columns are not here intended tok have any physical signiicance in the assembly of the apparatus andl their connections. The selection of a free circuit is effected b y the operation States Patent of the device of one co-ordinate of a set, e. g. a device common to a row, in which there is a free circuit and selecting the free circuit or one of the free circuits in the row corresponding to the operated row device by the operation of a device ot the other set of cti-ordinates, e. g. a device common to a column, the operation of the two devices marking a terminal or terminals indicative of the selected circuit. Continuing on the assumption that the co-ordinates represent rows and columns each circuit of a group in which selection is to be made is represented by a test terminal and the change in potential of this terminal may be utilised to denote a free or busy condition or" the circuit. Potential indicative of a free circuit may bring about a preparatory conditioning ot the device associated with the row in which the circuit is connected and when a demand for a free circuit arises an operating condition may then be applied to all the row devices so that one of the devices associated with rows in which there is a free circuit is operated to the exclusion oi the other row devices. Consequent on the operation of a row device a preparatory condition may be applied to the devices of columns in which there is a free circuit in the selected row and one of the column devices is operated to the exclusion of the others. The same principle may be extended to operate on a three co-ordinate basis, the devices being connected in rows, columns and in depth, a circuit being represented by a test terminal situated (diagrammatically) at the intersection of the three co-ordinates.

Circuit arrangements embodying the invention in which cold cathode gas discharge tubes are used are illustrated by way of example in the accompanying drawings to which the ensuing description refers. Fig. l of the drawings shows a two-coordinate arrangement, Fig. 2 shows how the marking terminals of Fig. l may be combined on a co-ordinate basis and Fig. 3 shows an element illustrative ci a three-co-ordinate arrangement.

Reference will first be had to Fig. i which shows an arrangement for making a selection among 25 circuits andmarking the selected circuit. It comprises ten threeelectrode cold cathode gas discharge tubes arranged in co-ordinate fashion, there being iive row tubes and tive column tubes. The row tubes are designated VTG--VT4 and the column tubes VUtl-VU4. The anode of a tube is indicated at A, the cathode at C, and the striker electrode at S. Each circuit is represented by a test terminal TT which is diagrammatically situated at the intersection of a row and a column, individual test terminals being designated by numerals representing the numbers of the row and the column at the intersection and a pair of marking terminals. Thus, the test terminal at the intersection of the top row and the left hand column is designated itil and that at the intersection of the top rowy and the second column from the left is designated 01 and so on. The marking terminals are connected to the cathode of the row and column tubes respectively, those associated with row tubes being designated Til-T4 and those associated with column tubes being designated Utl--Ufl Each test terminal is connected to the several cold cathode tubes over three connections, a irst connection over a rectifier and resistance to the striker electrode of the relevant row tube, the second, a connection over a resistance, a rectiiier and a further resistance to the cathode of the relevant row tube and the third, a connection over the lirst mentioned resistance in the cathode connection, a rectifier and further resistance vto the striker electrode of the column tube. The resistance, such as Rl in the connection to the striker electrode of the row tube is common to all the said iirst connections of the test terminals of a row and the further resistance, such as R2 in the connection to the cathode of the row tube is common to all the said second connections and lVT() will be the same.

the further resistance such as R3 in the connection to the striker electrode of the column tube is common to the said third connection of all test terminals in the same column. The said second and third connections from a test terminal include a resistance such as R4 common to the two connections. Rectiers such as MRI, MR2 and MR3 are included in the three connections respectively from the test terminal. The anodes of the row tubes are commoned and connected to a terminal GM, the common connection including resistance R7 and the anodes of the column tubes are likewise commoned and connected to terminal GM over a common resistance R8. The cathode of each tube in each set is connected to earth over a resistance such as resistance R5 for the row tubes and resistance R6 for the column tubes, and the cathodes are connected to the marking terminals Ti-Tli and Utl-U4 for the row and column tubes respectively.

The test terminals of all free circuits are marked by a potential above that required to ionise the respective row tubes and when a circuit becomes engaged the potential on the test terminal of that circuit is reduced below the ionising value. The common anode terminal GM, when no demand for a circuit in the group of twenty-five circuits exists is maintained at a potential below that necessary to maintain a discharge through a tube and when a demand exists the potential on terminal GM is raised to a value above that required to maintain a discharge through a tube but below that necessary for the tiring of a tube not already ionised. Thus, when a circuit in any particular row is free the row tube for that row will be ionised, but it will not be red unless the increased potential is present on terminal GM.

The selection and marking of a free circuit takes place as follows. It any circuit associated with a particular row is free, the potential on its test terminal is raised and the potential of the striker electrode of the row tube will be brought to the ionising valve. lf any of the circuits is the row are engaged, the rectiers in the connections of the test terminals of these circuits to the striker electrode of the row tube will be biased back by the potential on the test terminals of free circuits. The potentials of the column tubes, associated with free circuits will not be raised to the ionising value owing to the drop in the resistance such as R4 brought about by current flow in the circuit between the test terminal and the cathode of the row tube. As explained above, a row tube will not fire unless it has been previously ionised and a demand for a circuit exists. When such a demand takes place the potential of terminal GM is raised and one of the ionised row tubes will strike. The resultant drop in potential due to the presence of resistance R7 prevents more than one tube from firing. When a row tube lires the potential on the cathode rises and biases back the rectiiers such as MR?. of all the busy terminals in the row and the potential at the junction of the resistance such as R4 and rectiers MR2 and MR3 of the free terminals rises and the column tubes corresponding to the columns in which free circuits exist are ionised. As the potential of terminal GM has already been raised one of the ionised column tubes will tire, the others bein-g prevented from iiring due to the drop in potential owing to the inclusion of the common resistance R8 in their anode circuits. There is thus the condition that not.

until a row tube has tired can a column tube tire and that only one tube in each set can be in a tired condition at any one time. As an example, it may be assumed that the circuit connected to test terminal @il is free. In consequence tube VTS will be ionised. lf other circuits connected in the same row are free the condition of the tube Similarly, if the circuit connected to terminal 1G is free tube VTi will be ionised. There will be current through resistance R4, rectifier MR2, resistances R2. and R5 to earth thereby reducing the potential over rectifier MR3 on the striker electrode of tube VU below the ionising value for the tube. Similar conditions will apply as regard the column tubes for other free circuits in the rst and second rows counting from the top and any other row in which there is a free circuit. When the potential of terminal GM is raised tube VT or VT1 will fire. Let it be assumed that tube VT() lires. The potential of the cathode of this tube rises thereby allowing the potential of the lower point of resistance R4 to rise and tube VU will thereupon be ionised. At the same time other column tubes associated with columns in which a free circuit exists in the top row will be ionised. One of the ionised column tubes will tire owing to the potential on terminal GM and there will then be a row tube and a column tube associated with the circuit connected at the intersection of the row and column in a conducting condition. Let it be assumed that column tube VUO is fired. The increase in the cathode potential of tubes VTO and VUO will then appear on the marking terminals T0 and U0. It will thus be seen that in the above example, if the circuit connected to test terminal 01, for example is engaged, terminals T0 and U1 cannot be marked as the potential on the striker electrode of tube VU1 will be kept below the ionising value by reason of the reduction of potential on the terminal 01 and for a column tube of a column containing a free circuit to be tired the row tube of the row in which the free circuit exists must have previously been tired. When connection has been made with the selected circuit the potential on terminal GM is reduced but it will be immediately raised again if a demand for a circuit Within the group of 25 still exists.

The potentials appearing at the marking terminals T0-T4 and Utl- U4 may be caused to appear on a single marking terminal by a single co-ordinate arrangement as illustrated in Fig. 2. In that gure the terminals Til-T4 of the row tubes will be seen on the left and the terminals U0-U4 of the column tubes will be seen at the bottom of the ligure. Each row terminal and each column terminal is connected over a resistance to a common marking terminal, the resistances being individual to the terminals. Row terminal T0 and column terminal U0 will be seen to be connected over individual resistances to the common terminal TUOll. Similarly row terminal T0 and column terminal U1 are connected over other individual resistances to the common marking terminal TUOI and row terminal T1 and column terminal U0 are connected over yet other individual resistances to the common marking terminal TUl and so on.

It will be apparent that the number of circuits among which selection of a free circuit may be aiected is not limited to the number 25 as illustrated in Figs. 1 and 2 but that it can be extended to a greater number of circuits. If the circuits are numbered on a two-digit basis up to circuits may be grouped in the manner illustrated in these figures in which case there will be ten row tubes and ten column tubes.

Fig. 3 illustrates an extension of the principle described in Figs. 1 and 2 to selection by three groups of cold cathode tubes arranged in eiect in a 3-dimensional coordinate system. Such a system may be considered as comprising a number of row tubes in length, a number of column tubes in width and a number of tubes in depth, the test terminals being in eiect situated at the intersection of row, column and depth. In this figure which shows a single element for exemplary purposes, the tube VH may be looked upon as a row tube, the tube VT as a column tube and the tube VU as a depth tube. The similarity between the circuits as regards the row and column tubes of this iigure and those of Fig. l is apparent but it may be added that as the tube VU is not to be allowed to re until a VT tube has tired the additional resistances R9 and R13 are required so that the operations governing the tiring of tube VU with respect to tube VT are similar to those governing the tube VT with respect to tube VH. The anode resistance R12 and the cathode resistance R11 and striker electrode resistance avancee R associated with tube VU will be seen to correspond to the similarly connected resistances of the other tubes. The circuit corresponding to the test terminal TT will be indicated by positive potential on the marking terminals H, T and U and these potentials may be caused to appear on a single marking terminal by an extension of the principle illustrated in Fig. 2.

What is claimed is:

l. Circuit arrangements for the selection of a free circuit among a number of circuits, comprising test terminals of the circuits among which selection is to be made situated at the intersection of the co-ordinates of rows and columns, negative resistance devices connected Ato rows and columns, there being one device for each row connected to all the test terminals in the row and one device tor each column connected to all the test terminals in the column, means for operating the device or a row dependent on there being a free test terminal situated in the row, means for operating the device of a column containing a free test terminal at the intersection of said cuit among a number of circuits, comprising test terminals o oi the circuits among which sclecti-on is to be made situated at the intersection of the coordinates of rows and columns, negative resistance devices connected to rows and columns, there being one device for each row connected to all the test terminals in the row and one device for each column connected to all the test terminals in the column, means for bringing the devices of rows in which there is a free circuit into a preparatory condition, means for completing the operation of lone of said row devices to the exclusion of the others and for bringing into a preparatory condition the devices of all the columns containing a free test terminal in the row for which the row device has been operated and for operating one of said column devices to the exclusion of the others depending on the prior operation of a row device, marking terminals of circuits corresponding to said test terminals, and means dependent on the operation of a row device and a column device for applying a distinctive potential to the marking terminal corresponding to the free test terminal situated at the intersection of the row and column containing said operated devices.

3. Arrangements as in claim 2, in which the negative resistance devices are three-electrode gas-filled electric discharge tubes and each test terminal is connected on the one hand to a source of ionising potential and on the other hand to the striker electrode of the row tube and to the striker electrode of the column tube, the anodes of all the row tubes being connected over one impedance to a source of firing potential and the anodes of all the column tubes being connected over another impedance to the same source of tiring potential, and including means for holding the potential on the striker electrode of a column tube below the ionising value for the tube, means for raising said potential to its ionising value on the tiring of a row tube, and individual resistances connected in the cathode circuits of all the tubes, the junction of the cathode of a tube and its individual resistance being connected to a marking terminal.

4. Arrangements as in claim 3, in which the connection v of a test terminal to the striker electrode of a row tube includes a rectifier individual to the test terminal and a resistance common to all the test terminals of the row and in which the connection of a test terminal to the cathode of a row tube includes a resistance and a rectifier individual to the test terminal and a resistance common to all the test terminals of the row and in which the connection of a test terminal to the striker' electrode of a column tube includes said individual resistance, a further rectier individual to the test terminal and a resistance common to all the test terminals of a column, all the rectiiiers being poled similarly to present a low resistance to current flow from a test terminal towards the discharge tubes.

5. Arrangements as in claim l, in which there is a marking terminal individual to each row and a marking terminal individual to each column, said marking terminals being connected to rows and columns of a further coordinate system, the intersection of a row and a column in said further co-ordinate system being connected over individual resistances to a common marking terminal corresponding to the test terminal situated at the intersection of the row and column connected to said individual marking terminals.

6. Arrangements as in claim l, in which the test terminais are situated at the intersections of three co-ordinates, there being row devices and column devices and a further set of negative resistance devices, the operation -of a device in the further set being dependent on the prior operation ot' a column device in the same manner as the operation of a column device is dependent on the prior operation of a row device, and in which there are three sets of marking terminals, one set for each co-ordinate, and marked respectively by the operation of the negative resistance devices of the three co-ordinates of a free test terminal.

References Cited in the tile of this patent UNITED STATES PATENTS 2,629,020 Robertson Feb. 17, 1953 

